Nachiappan Valliappan & Rajaganesh Ganesh The University of Texas at Austin
45
EE 381V Wireless Communications Lab Graduate Course Project PAPR Reduction Techniques in OFDM Systems Nachiappan Valliappan & Rajaganesh Ganesh The University of Texas at Austin
description
EE 381V Wireless Communications Lab Graduate Course Project PAPR Reduction Techniques in OFDM Systems. Nachiappan Valliappan & Rajaganesh Ganesh The University of Texas at Austin. Objectives. Understand the effects of high PAPR in multicarrier systems - PowerPoint PPT Presentation
Transcript of Nachiappan Valliappan & Rajaganesh Ganesh The University of Texas at Austin
EE 381V Wireless Communications Lab
Graduate Course Project
PAPR Reduction Techniques in OFDM Systems
Nachiappan Valliappan & Rajaganesh Ganesh
The University of Texas at Austin
Objectives
Understand the effects of high PAPR in multicarrier systems
Investigate performance of available PAPR reduction techniques
Identify criterion for PAPR reduction technique selection
Instrument SpecsNI 5660 – RF Signal Analyzer Input power +30 to -130 dBm (provides up
to 50 dB of input attenuation) Digitizer 64MS/s
NI 5670 – RF Vector Signal Generator• Output average power -145dBm to +13dBm• Maximum allowable peak envelope power
+17dBm• 1dB Gain Compression point dependent on
temperature, frequency etc.
Instrument SpecsNI 5670 – RF Vector Signal
Generator
Table 1 [1]
System DesignSymbol rates supported
1Msps, 2Msps,5Msps,10Msps,12.5Msps
Channel codingRate 2/3 convolutional code
Modulation schemes supportedBPSK, 4-QAM, 16-QAM
Pulse ShapingRaised cosine pulse shape with roll-off 0.5
System DesignPassband Bandwidth
1MHz, 2MHz, 5MHz, 10MHz, 12.5MHz
Number of subcarriers N (= FFT Size)64
Length of Cyclic Prefix Lc
16
PAPR Oversample Factor4
System DesignSymbol Timing Extraction
Max Energy, Early-Late Gate Method
Frame Timing & Frequency Offset Estimation Schmidl-Cox Algorithm
Channel Estimation & Equalization IEEE 802.11a training sequence
PAPR Reduction TechniquesInterleaving
Amplitude Clipping & Filtering (RCF)
Selection Level Mapping (SLM)
Partial Transmit Sequence (PTS)
Active Constellation Exchange (ACE)
Tone Injection
Experiment I
PAPR Measurement for unusually high PAPR Signals
Procedure
Loop back Tx-Rx by an RF cableSend a sequence of all ones (1’s) so that
the max. theoretical PAPR is reached
(N – Number of subcarriers)Oversample the Rx signal & calculate
PAPRCompare observed PAPR with theoretical
results for the different schemes
Max. PAPR = 10*log10(N)
System Setup for Expt. IData: All 1’s sequenceSymbol Rate: 1 MspsModulation scheme: 4-QAM N=64, Lc=16No channel coding
Tx average power level = - 2.2dBmPEP is just below 17dBm!
Rx reference level = 20dBm
Experiment I
Results
Effect of PA saturation In-band distortion1dB compression point 13dBm @ 2.7G, 16dBm @ 2G
@2GHz @2.7GHz
No PAPR scheme
RCF
Interleaving
SLM
PTS
ACE
Experiment II
PAPR Measurement of a typical OFDM signal
Complementary CDF (CCDF) comparison
Procedure
Loop back Tx-Rx. by an RF cableSend a sequence of random bitsOversample the Rx signal & calculate
PAPR for the different schemesPlot the CCDF at Tx & RxObserve reduction in PAPRObserve changes to Tx constellation
System Setup for Expt. IIData: Random bitsSymbol Rate: 1 MspsModulation scheme: 4-QAM N=64, Lc=16No channel coding
Tx average power level = -40dBm
Rx reference level = -20dBm
Experiment II
Results
RCF
Effect of Tx Power Spectrum
Before RCF After RCF
Effect on Tx Constellation
Interleaving
SLM
PTS
ACE
Effect on Tx Constellation
Tone Injection
Effect on Tx Constellation
Experiment III
A typical OFDM system with PAPR reduction
Procedure
Transmit random bits over the wireless channel
Perform synchronization, offset, channel estimation & equalization
Find the BER for uncoded transmissions
Observe the impact of in-band distortion (esp. in RCF!) on BER
Experiment III Results
5MHz Bandwidth
10MHz Bandwidth
12MHz Bandwidth
BER vs SNR - Uncoded 4-QAM
PAPR Techniques
- A Comparative Study
Table 2 [7]
Technique Distortionless
Power Increase
Data rate loss
RCF No No NoInterleaving Yes No YesSLM Yes No YesPTS Yes No YesTone Injection Yes Yes NoACE Yes Yes No
Tradeoff
Table 2 [6]
Technique Processing at Tx & RxRCF Tx: Amplitude clipping, filtering
Rx: None
Interleaving Tx: K IDFTs, (K – 1) interleavingsRx: Side information extraction, inverse interleaving
SLM Tx: U IDFTsRx: Side information extraction, inverse SLM
PTS Tx: M IDFTs, WM–1 complex vector sumsRx: Side information extraction, inverse PTS
Tone Injection Tx: IDFTs, search for maximum point in time, tones to be modified, value of p and qRx: Modulo-D operation
ACE Tx: IDFTs, projection onto “shaded area”Rx: None
Table 3 [7]
References[1] National Instruments, NI RF Signal Generator: NI PXI-5670/5671
Specifications, Retrieved December 3, 2010 from http://www.ni.com/pdf/manuals/371355c.pdf
[2] National Instruments, 2.7 GHz RF Vector Signal Analyzer, Retrieved December 2, 2005 from http://www.ni.com/pdf/products/us/4mi469-471.pdf
[3] National Instruments, NI RF Signal Generator: Getting Started Guide, Retrieved December 1, 2005 from http://www.ni.com/pdf/manuals/371356b.pdf
[4] National Instruments, NI 5670 RF Vector Signal Generator User Manual, Retrieved December 1, 2005 from http://www.ni.com/pdf/manuals/rfsg _um.pdf
[5] National Instruments, 2.7 GHz RF Vector Signal Analyzer, Retrieved December 2, 2005 from http://www.ni.com/pdf/products/us/4mi469-471.pdf
References[6] National Instruments, NI RF Signal Analyzer: Getting Started Guide,
Retrieved December 2, 2005 from http://www.ni.com/pdf/manuals/371237a.pdf
[7] Jae Hong Lee and Seung Hee Han. An overview of peak-to-average power ratio reduction techniques for multicarrier transmission Wireless Communications. IEEE Wireless Communications Magazine, Vol. 12:pp 56-65, April 2005.
